1. Field of the Invention
The present invention relates to controlling of hybrid drives.
2. Description of Related Art
Hybrid drives combine an electric motor and an internal combustion engine, which form the drive of a vehicle when combined in various ways. Whereas the electric motor is suitable for covering dynamic load peaks and for energy recovery in braking, the internal combustion engine is used to convert fuel and offers a high power output, in particular for high speeds and high driving performance. Depending on the driver's intent and traffic conditions, it may be necessary with regard to efficiency or with regard to the desired driving performance to turn on the internal combustion engine as a drive in addition to the operation of the electric motor or, if both drive systems (electric motor and internal combustion engine) are in use, to turn off the internal combustion engine (for example, to save fuel). Furthermore, there are basically two other drive modes: (1) neither of the two systems is used for the drive, and (2) only the internal combustion engine is used for the drive. These two drive modes (1) and (2) are not the focus of the present invention. The present invention relates in particular to a control for the operating modes in which only the electric motor (only-electrical operation) or the electric motor together with the internal combustion engine (combination operation) is used as the drive system.
In switching between these two operating modes (only-electrical operation, combination operation), jerky movements result. When the internal combustion engine is added while the electric motor is driving, and when the internal combustion engine is turned off when both drive systems (internal combustion engine and electric motor) are in use, jerky movement results due to a sudden drop in driving torque. When the internal combustion engine is added, for example, in parallel hybrid drives in which the electric motor is also used as the starter for the internal combustion engine, the jerky movement is caused by the fact that the electric motor is used not only for the drive but must also provide power for starting the internal combustion engine. The torque required for starting is thus suddenly no longer available for the drive. Furthermore, when the internal combustion engine is stopped, there is a sudden drop in the driving torque of the hybrid drive by the amount previously supplied by the internal combustion engine for the drive. Both cases may result in jerky movements, which definitely have a negative effect on driving performance. This is unpleasant with very heavily loaded vehicles and/or steeply inclined roadways in particular and may also result in hazardous traffic situations, among other things.
However, according to the related art, a change signal, which originates from a driver or from a drive control, is converted directly without estimating the consequences of the change in drive mode.
Published European patent document EP 1469195 B1 describes a method for automatic shutdown of an internal combustion engine, first signaling to the driver the intended shutdown before the automatic shutdown. The driver then has a certain interval of time to actively suppress the planned shutdown of the internal combustion engine by setting an appropriate switch. First, this requires the active involvement of the driver, so the latter may be distracted from the traffic flow, and second, it is up to the driver to judge the consequences of the shutdown, which results in a substantial source of error.
An object of the present invention is therefore to provide a control mechanism for the drive mode of a hybrid drive using which a better driving performance may be implemented.